Uncertain future: Kudrow and Schwimmer (back, second and third from left)

Friends stars David Schwimmer and Lisa Kudrow - Ross and Phoebe in the hit US comedy - are said to be planning to leave the show.

The report, in a British newspaper, comes days after Channel 4 outbid Sky to secure the first-run rights to the sitcom and hospital drama ER from 2001 in a £100m deal.

The duo play two of the six core characters in the show, following the lives of a group of New York twenty-somethings.

The Independent newspaper claims Sky lost interest in retaining the rights to Friends after managing director Elisabeth Murdoch heard from insiders at Warner Brothers, which makes the show, that Schwimmer and Kudrow were leaving.

At the time, Murdoch claimed the asking price was too high and that Sky was more interested in "developing British franchises".

Elisabeth Murdoch: Reportedly lost interest in the show

Friends was first shown in the UK on Channel 4, although Sky bought the rights to it in 1996. But Channel 4 has continued to show the series, albeit a few weeks after it is shown on Sky One, and it is still one of the network's most popular series.

Now C4 has regained the rights to it, it has been suggested it could show it on its planned paid-for entertainment channel, E4.

But the loss of a two of the central characters could make the series, a hit around the world, less of an attraction to viewers. The two have been in the series, along with Jennifer Aniston, Courteney Cox, Matt LeBlanc and Matthew Perry, since it launched in 1994.

However, it has had a history of cast disputes. In 1996, the cast threatened to go on strike unless they received pay increases, and 12 months ago they were paid a Christmas bonus of $200,000 (£125,000) designed to keep them with the series.

For the sixth series, which ended in November, the cast were reportedly offered $250,000 (£155,000) per episode.

Warner Brothers in the US dismissed the story of Schwimmer and Kudrow's departure as "a rumour".

A Channel 4 spokesman is quoted as saying: "Periodically people do leave the series because of disputes over pay or whatever. We are not saying this isn't true".